Depolymerization of the Glutenin Macropolymer During Mixing: II. Differences in Retention of Specific Glutenin Subunits

The depolymerization of individual high and low molecular weight (HMW and LMW, respectively) glutenin subunits (GS) from the glutenin macropolymer (GMP) in doughs during mixing was investigated by reversed-phase (RP) HPLC and SDS-PAGE. Cultivars with different dough strengths, as well as lines null for specific HMW-GS and biotypes differing at individual HMW-GS and LMW-GS encoding loci, were studied. During mixing, the proportion of total HMW-GS in GMP decreased, and the ratios of different subunits in the GMP in doughs changed. There was a loss of chromosome 1B- and 1D-encoded x-HMW-GS, while the relative proportions of y-HMW-GS (among HMW-GS) increased. Changes in 1B subunits occurred first, while most of the changes in 1D HMW-GS content occurred during dough breakdown. Changes were more pronounced for doughs of weak to average strengths than for stronger doughs. RP-HPLC analysis demonstrated a consistent increase in the retention times (surface hydrophobicity) of chromosome 1D-encoded HMW-GS but not of other HMW-GS or LMW-GS during mixing. SDS-PAGE and RP-HPLC demonstrated that specific B subunits, typically those with lower hydrophobicity, were selectively depolymerized from the GMP during dough breakdown, while the proportions of specific C subunits, typically those with greater hydrophobicity, increased. Similar trends were seen in analyses of several pairs of biotypes differing at single LMW-GS encoding loci, although there were slight differences in the depolymerization behavior of wheats with different allelic compositions. The results suggest that dough breakdown may be triggered by the loss of specific HMW-GS from the GMP, and a structural hierarchy may exist for different LMW-GS within glutenin in doughs.     

Changes in SDS Solubility of Glutenin Polymers During Dough Mixing and Resting

An online coupling of high‐performance size‐exclusion chromatography (HPSEC) combined with multiangle laser‐light scattering (MALLS) and a reverse‐phase HPLC procedure were used to characterize and reveal the polydispersity of the glutenin polymers of doughs during mixing and resting. Experiments involved doughs prepared from several samples of a common French wheat cultivar (Soissons) differing in total amount of SDS‐unextractable glutenin polymers. During dough mixing, the amounts, size distribution of protein, and glutenin subunit composition within the SDS‐unextractable polymers changed. However, the major changes in SDS‐unextractable glutenin content and size distribution occurred before the peak mixing time (MT) was reached, whereas detectable changes in subunit composition also occurred after the peak MT. Even if sonication, which was used to solubilize the total wheat glutenin, can narrow the glutenin size distribution, HPSEC‐MALLS revealed a close relationship between the SDS solubility of the glutenin polymers and size distribution, confirming a depolymerization and repolymerization hypothesis. During the depolymerization of the SDS‐unextractable polymers, glutenin subunits were released in nonrandom order, which indicated that the polymers have a hierarchical structure. Some HMW glutenin subunits (HMW‐GS), especially 1D×5, were particularly resistant to the depolymerization mechanism. This suggested that the subunit plays a major role in forming the backbone of the SDS‐unextractable polymers, consistent with the potential to form branched structure. These studies suggest that the SDS‐unextrac‐table polymers in flours have a well‐ordered structure that can be modified by dough mixing and resting.     

Effect of Single Substitution of Glutenin or Gliadin Proteins on Flour Quality of Alpha 16, a Canada Prairie Spring Wheat Breeders' Line

The effect of genetic variation in the glutenin and gliadin protein alleles of Alpha 16, a Canada Prairie Spring (CPS) wheat line, on the dough mixing, bread, and noodle quality properties were evaluated. The presence of a gliadin component (BGGL) and the low molecular weight glutenin subunit (LMW-GS) 45 found in the selection Biggar BSR were associated with significant increases in dough strength characteristics. The results of the study showed that gliadins, LMW-GS, and high molecular weight glutenin subunits (HMW-GS) can influence bread- and noodle-making properties of wheat flour. Genotype-by-environment interactions were not significant for most of the quality parameters studied, indicating that the differences observed in quality characteristics were mainly due to the effect of genotype.     

Molecular Weight Distribution of Wheat Proteins

The molecular weight distribution (MWD) of wheat proteins is becoming recognized as the main determinant of physical dough properties. Studies of high polymers have shown that properties such as tensile strength are related to a fraction of polymer with molecular weight above a critical value and the MWD of this fraction. Elongation to break is treated as a kinetic process with energies of activation for breaking noncovalent bonds and for chain slippage through entanglements. These considerations are related to tensile properties of wheat flour doughs such as those measured by the extensigraph. The MWD of wheat proteins is determined by the relative amounts of monomeric and polymeric proteins and the MWD of the polymeric proteins. The latter, in turn, depends on the ratio of high molecular weight glutenin subunits (HMW-GS) to low molecular weight glutenin subunits (LMW-GS), the specific HMW-GS that result from allelic variation, and the presence of modified gliadins that act as chain terminators. The role of these compositional variables in determining dough extensional properties is discussed in terms of present knowledge. Determination of MWD of wheat proteins is hindered by the difficulty of their solubilization and the lack of methods for reliably measuring very high molecular weights. Among the promising techniques for achieving these measurements are multiangle laser light scattering (MALLS) and field flow fractionation (FFF).     

Comparative study of the effect of incorporated individual wheat storage proteins on mixing properties of rice and wheat doughs

The aim of this work was to compare the effects of incorporated wheat storage proteins on the functional properties of rice and wheat flours. The advantage of rice as a base flour compared to wheat is that it does not contain any wheat flour components and, therefore, has no interactive effect between wheat glutenin proteins. The incorporation of individual HMW glutenin subunit proteins (Bx6, Bx7, and By8) in different ratios had significant positive effects on the mixing requirements of both rice and wheat doughs. Reconstitution experiments using two x+y type HMW-GS pairs together with a bacterially expressed LMW-GS have been also carried out in this study. The largest effects of polymer formation and mixing properties of rice flour dough were observed when Bx and By subunits were used in a 1:1 ratio and HMW and LMW glutenin subunits in a 1:3 ratio. However, using the same subunit ratios in wheat as the base flour, these synergistic effects were not observed.     

Purification and Characterization of the Glutenin Subunits of Triticum tauschii,Progenitor of the D Genome in Hexaploid Bread Wheat

N-terminal amino acid sequences and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) molecular weights have been determined for high-performance liquid chromatography (HPLC)-purified high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits (GS) of Triticum tauschii ssp. strangulata, contributor of the D genome to hexaploid bread wheat. The use of three different extraction procedures resulted in similar glutenin preparations. On the basis of N-terminal sequences, the same types of glutenin subunits that have been reported in bread and durum wheats (HMW-GS of both the x and y types and LMW-GS of the LMW-s, LMW-m, α-, and γ-types) were found in T. tauschii. However, the HMW-GS in T. tauschii were in greater proportion relative to LMW-GS when compared to reported values for a bread and durum wheat. Our results support the likelihood that differences in the proportions of the various subunits contributed by the A, B, and D genomes, rather than qualitative differences in the types of subunits, are responsible for the major differences in quality characteristics between bread wheat and durum wheat.     

Preparative Method for In Vitro Production of Functional Polymers from Glutenin Subunits of Wheat

An in vitro method for preparative‐scale production of artificial glutenin polymers utilizes a controlled environment for the oxidation of glutenin subunits (GS) isolated from wheat flour to achieve high polymerization efficiency. The functionality of in vitro polymers was tested in a 2‐g model dough system and was related to the treatment of the proteins before, during, and after in vitro polymerization. When added as the only polymeric component in a reconstituted model dough (built up from gliadin, water solubles, and starch fractions), in vitro polymers could mimic the behavior of native glutenin, demonstrating properties of dough development and breakdown. Manipulating the high molecular weight (HMW)‐GS to a low molecular weight (LMW)‐GS ratio altered the molecular weight distribution of in vitro polymers. In functional studies using the 2‐g mixograph, simple doughs built up from homopolymers of HMW‐GS were stronger than those using homopolymers of LMW‐GS. These differences may be accounted for, at least in part, by different polymer size distributions. The ability to control the size and composition of glutenin polymers shows the potential of this approach for investigating the effects of glutenin polymer size on dough function and flour end‐use quality.     

Isolation and Functionality Testing of Low Molecular Weight Glutenin Subunits

Various protein fractionation techniques have been applied to the isolation and purification of milligram quantities of low molecular weight glutenin subunits (LMW-GS). No single technique was applicable to the purification of the majority of the subunits. Partial purification of certain LMW-GS was obtained using ion-exchange chromatography and reversedphase HPLC. Preparations containing α- and γ-type subunit sequences did not strengthen dough when incorporated into a base flour, whereas preparations containing a subunit with an N-terminal methionine residue (METSHIPGL-) did. Using preparative isoelectric focusing over a narrow pH range, it was possible to purify (to ≈90% purity) a B subunit that also had the N-terminal sequence of METSHIPGL-. This polypeptide, when incorporated into a base flour, had a dough strengthening effect in mixing trials, but less so than an equivalent amount of a high molecular weight glutenin subunit.     

The Combination of Rhizopus chinensis Lipase and Transglutaminase Affects the Rheology and Glutenin Macropolymer Properties of Frozen Dough

The combination of Rhizopus chinensis lipase (RCL) and transglutaminase (TG) was previously reported to improve the quality of frozen dough bread. In this study, the effects of RCL, TG, and their combination on the modification of glutenin macropolymer (GMP) and rheological properties of dough during frozen storage were investigated. Frozen storage changed both GMP and rheology properties of dough. TG treatment significantly decreased the ratio of high‐molecular‐weight glutenin subunits to low‐molecular‐weight glutenin subunits and GMP content in fresh dough, and GMP particle size increased. The effect of RCL on GMP properties was not significant, but its combination with TG dramatically increased the proportion of the larger particles and weighted average volume (D_4.3) in GMP. The treatment with the enzyme combination could have inhibited the depolymerization of GMP, which slowed down the decrease rate of some parameters such as GMP content, proportion of larger particles, D_4.3, and release of free amino and thiol groups during frozen storage. The modification of GMP properties by enzyme treatment weakened the effect of the freezing process on rheological properties of dough, especially TG treatment and its combination with RCL. Correlation between GMP particle size and dough properties (dough tensile force and elastic modulus) after freezing and enzyme treatment were confirmed.     

Immunocytochemical Localization of Gluten Proteins Uncovers Structural Organization of Glutenin Macropolymer

The content and composition of the disulfide‐bonded glutenin macropolymer has been shown to influence dough properties, although its structural organization is poorly characterized. The structure of the glutenin macropolymer in dough was studied using an immunolocalization transmission electron microscopy (TEM) technique by localizing gliadins, low molecular weight glutenin subunits (LMW‐GS), and high molecular weight glutenin subunits (HMW‐GS) in sections of dough using antibody probes selective for each of the three classes of gluten polypeptides. Distinct differences in the distribution patterns of gliadins, LMW‐GS, and HMW‐GS were observed, which suggests that proteins have different roles in the structural organization of the gluten matrix. On the basis of the observed distribution of the proteins in dough, it is speculated that gliadins, which are randomly distributed as individual particles, fill space within the glutenin macropolymer; LMW‐GS, which are present as clusters, are speculated to form aggregated branch structures; and HMW‐GS, which are present as chains, are speculated to form a network from which the LMW‐GS branches are formed. Changes in the distribution of gliadins, LMW‐GS, and HMW‐GS in dough during mixing were also noted. Such an arrangement supports previous biochemical evidence which has established that gliadins, LMW‐GS, and HMW‐GS have specific roles in the structural organization of the glutenin macropolymer in doughs.     

Effects of Wheat Bug (Eurygaster maura) Protease on Glutenin Proteins

Proteolytic degradation of 50% 1-propanol insoluble (50PI) glutenin of six common wheat cultivars by wheat bug (Eurygaster maura) protease was investigated using reversed-phase HPLC. Wheat at the milk-ripe stage was manually infested with adult bugs. After harvest, bug-damaged kernels were blended (2:1, kernel basis) with undamaged grain of the same cultivar. Samples of ground wheat were incubated in distilled water for different times (0, 30, 60, and 120 min). The incubated whole meal samples were subsequently freeze-dried and stored until analysis. The degree of proteolytic degradation of 50PI glutenin was determined based on the quantity of total glutenin subunits (GS), high molecular weight GS (HMW-GS), and low molecular weight GS (LMW-GS). For ground wheat samples incubated for ≥30 min, 50PI glutenin was substantially degraded as evidenced by a >80% decrease on average in total GS, HMW-GS, and LMW-GS. Some cultivars showed different patterns of glutenin proteolysis as revealed by differences in the ratios of HMW-GS to LMW-GS between sound and bug-damaged samples; a significant decrease in this ratio was found for four cultivars. This evidence, combined with other observations, indicated that there were intercultivar differences in polymeric glutenin resistance to the protease of the wheat bug Eurygaster maura. While the nature of this resistance is unknown, it should be possible to select and develop wheat cultivars with improved tolerance for wheat bug damage. Propanol insoluble glutenin, which corresponds to relatively large glutenin polymers, appears to be an excellent quantitative marker for this purpose.     

Glutenin Macropolymer in Salted and Alkaline Noodle Doughs

An attempt was made to understand the physicochemical attributes that are the basis of physical differences between alkaline and salted noodle doughs. Flour and dough properties of one soft and three hard‐grained wheat cultivars were observed. Doughs were made with either sodium chloride or sodium carbonate. Each formulation variant was tested at both high and low water additions. Samples for glutenin macropolymer (GMP) isolation were taken at selected noodle dough processing stages. When a 1.67% w/v Na₂CO₃ solution was used for mixograph testing, dough characteristics were radically altered and differences between cultivars were masked. In lubricated squeezing flow (LSF) testing, hard wheat noodle doughs had significantly (P < 0.01) longer relaxation times and higher % residual force values than soft wheat doughs in both the salted and alkaline variants. LSF maximum force and biaxial viscosity were significantly higher in alkaline doughs than salted. GMP extracted from alkaline doughs was gummy and sticky, and was more opaque than GMP from salted doughs. GMP weight decreased sequentially when extracted from samples taken in the active phase (mix, compound, sheet) of noodle dough processing and decreased more in alkaline doughs. GMP weight increased more after 24 hr of dough rest in salted doughs. GMP gel strength was noticeably higher in GMP extracted from alkaline doughs. After dough resting, alkaline GMP gel strength significantly increased, whereas it decreased in GMP from salted doughs, suggesting a role for GMP in the increased stiffness of alkaline noodle doughs.     

施氮量对小麦氮代谢相关酶活性和子粒蛋白质品质的影响

在2003～2004年和2004～2005年小麦生长季,以强筋小麦济麦20为材料,分别设置N 0、96、168、240、276 kg/hm2 5个施氮量处理和0、96、168、240 kg/hm2 4个施氮量处理,研究不同施氮量对小麦氮代谢相关酶活性和子粒蛋白质品质的影响。两年度的试验结果均表明,在一定施氮量范围内,随施氮量增加,公顷穗数、穗粒数、蛋白质含量、子粒产量和蛋白质产量均显著升高;继续增加施氮量子粒产量显著降低,公顷穗数、穗粒数、蛋白质产量降低或无显著差异。其中2004～2005年生长季,在0～168 kg/hm2施氮量范围内,随施氮量增加,旗叶谷氨酰胺合成酶（GS）活性、开花21d后的旗叶內肽酶（EP）活性、旗叶游离氨基酸含量、子粒醇溶蛋白含量、高分子量谷蛋白亚基（HMW-GS）和低分子量谷蛋白亚基（LMW-GS）含量、HMW-GS / LMW-GS比值、子粒蛋白质含量、公顷穗数和穗粒数、子粒产量均显著升高,面团形成时间和稳定时间延长;继续增加施氮量至240 kg/hm2,GS活性无显著变化,但开花21 d后的EP活性、-醇溶蛋白、-醇溶蛋白、HMW-GS、LMW-GS和子粒蛋白质含量仍显著提高,面团稳定时间继续延长,子粒产量显著降低。说明施氮过多对小麦氮素同化和产量无益;提高开花后旗叶GS活性和灌浆后期旗叶EP活性,有利于HMW-GS和LMW-GS的积累及HMW-GS/ LMW-GS比值的提高。适量施氮不仅提高了子粒灌浆所需氮源的供给能力,而且显著增加公顷穗数和穗粒数,扩大了单位面积库容,增加了单位面积上的氮素和光合产物在子粒中的贮存,这是适量施氮实现子粒品质和产量同步提高的生理原因。本试验条件下高产优质高效的施氮量为168～240 kg/hm2。     

Genetic characteristic of high molecular weight glutenin subunits in somatic hybrid wheat lines -- potential application to wheat breeding

Analysis of 17 derivatives from a somatic fusion between common wheat (Triticum aestivum) and tall wheat grass (Thinopyrum ponticum) showed a diversity of high molecular weight glutenin subunit (HMW-GS) compositions. On the basis of the inheritance of HMW-GS patterns, the derivatives were either (i) bred true over four successive generations, (ii) generated a few novel HMW-GS combinations at each generation, or (iii) showed highly unstable HMW-GS compositions. HMW-GS analysis of F(5) seed and each single seed-generated F(6) progenies further revealed that most of the HMW-GS had genetic stability. The variations of HMW-GS were inferred to occur in early generations and were maintained thereafter. Low molecular weight glutenin subunits (LMW-GS) in hybrid lines with high or low bread-making quality, classified into the first pattern, were compared. The result showed that hybrid lines with the uniform HMW-GS patterns also have identical LMW-GS patterns. The Glu-1 quality score was inferred to be relatively significant to the sodium dodecyl dulfate sedimentation value, as well as to correlate with the gluten exponent and contents of dry gluten and proteins. Sexual hybridization between high-quality somatic hybrid progeny II-12 and Chinese Spring (CS) showed that these high-quality HMW-GS genes could entail progenies. There was not subunit variation in the progenies of II-12 x CS. Therefore, sexual hybridization between somatic hybrid line and cultivars can transfer novel high-quality HMW-GS of somatic hybrids and benefit wheat breeding.     

施氮量对不同品质类型小麦子粒蛋白质组分含量及加工品质的影响

选用强筋小麦济麦20、中筋小麦泰山23和弱筋小麦宁麦9号,利用反相高效液湘色谱（RP-HPLC）方法测定了施氮量对不同品质类型小麦子粒蛋白质组分含量和高分子量谷蛋白亚基（HMW-GS）、低分子量谷蛋白亚基（LMW-GS）含量的影响,并分析其与子粒加工品质的关系。结果表明,随施氮量增加,强筋小麦济麦20和中筋小麦泰山23的子粒蛋白质含量及各组分含量均呈先增加后降低的趋势,施氮量为N 240 kg/hm2时,蛋白质各组分含量较高,加工品质较好; 过量施氮抑制了HMW-GS合成,这是过量施氮导致强筋和中筋小麦子粒蛋白质品质变劣的原因之一。随施氮量增加,弱筋小麦宁麦9号子粒的蛋白质各组分含量显著增加,加工品质变劣。增施氮肥,3个品种的谷蛋白和醇溶蛋白含量的增加幅度显著高于清蛋白+球蛋白含量,这是施氮改善强筋和中筋小麦子粒加工品质的主要原因。济麦20和泰山23两品种的总蛋白质含量及醇溶蛋白含量无显著差异,但强筋小麦济麦20的谷蛋白含量、贮藏蛋白、HMW-GS、LMW-GS、谷蛋白大聚合体（GMP）含量及谷蛋白与醇溶蛋白含量的比值（Glu/Gli）和HMW-GS与LMW-GS含量的比值（HMW/LMW）高于中筋小麦泰山23,这是强筋小麦济麦20加工品质形成及其面团形成时间和稳定时间显著高于泰山23的重要原因。     

Differing Effects of Mechanical Dough Development and Sheeting Development Methods on Aggregated Glutenin Proteins

Dough development using sheeting and mechanical dough development (MDD) were compared with respect to the effect the mixing method had on the molecular size distribution and degree of protein thiol exposure of the aggregated glutenin proteins. Although sheeting imparts a lower rate of work input on doughs than does MDD mixing, changes in protein aggregation patterns during mixing were similar for both methods of dough development, indicating that protein disaggregation was important in the process of dough development. In both systems, a reduced rate of change in the protein aggregation patterns was associated with optimum dough development. The MDD mixing was characterized by increasing exposure of the thiol groups on the SDS‐insoluble glutenin during mixing while the sheeting process resulted in fewer exposed thiol groups on both SDS‐soluble and SDS‐insoluble glutenin proteins. This suggested that disulfide bond rupture may not be a required process in dough development and that high effective stresses per se may not be required to develop doughs. This is consistent with a model for dough development that does not require extensive covalent bond rupture but instead involves mainly rupture and reformation of noncovalent interactions such as hydrophobic bonds and hydrogen bonds between protein chains.     

Role of Gluten and Its Components in Determining Durum Semolina Dough Viscoelastic Properties

Gluten was isolated from three durum wheat cultivars with a range in strength. Gluten was further fractionated to yield gliadin, glutenin and high molecular weight (HMW) and low molecular weight (LMW) glutenin subunits (GS). The gluten and various fractions were used to enrich a base semolina. Enriched dough samples were prepared at a fixed protein content using a 2‐g micromixograph. Mixing strength increased with addition of gluten. Dynamic and creep compliance responses of doughs enriched with added gluten ranked in order according to the strength of the gluten source. Gliadin addition to dough resulted in weaker mixing curves. Gliadin was unable to form a network structure, having essentially no effect on dough compliance, but it did demonstrate its contribution to the viscous nature of dough (increased tan δ). Source of the gliadin made no difference in response of moduli or compliance. Addition of glutenin to the base semolina increased the overall dough strength properties. Glutenin source did influence both dynamic and compliance results, indicating there were qualitative differences in glutenin among the three cultivars. Enrichment with both HMW‐GS and LMW‐GS increased overall dough strength. Source of HMW‐GS did not affect compliance results; source of LMW‐GS, however, did have an effect. The LMW‐2 proteins strengthened dough to a greater extent than did LMW‐1. Mechanisms responsible for dough viscoelastic properties are described in terms of reversible physical cross‐links.     

Prolamin aggregation, gluten viscoelasticity, and mixing properties of transgenic wheat lines expressing 1Ax and 1Dx high molecular weight glutenin subunit transgenes

The composition of high molecular weight (HMW) subunits of glutenin determines the gluten strength and influences the baking quality of bread wheat. Here, the effect of transgenes coding for subunits 1Ax1 and 1Dx5 was studied in two near-isogenic wheat lines differing in their HMW subunit compositions and mixing properties. The subunits encoded by the transgenes were overexpressed in the transformed lines and accounted for 50-70% of HMW subunits. Overexpression of 1Ax1 and 1Dx5 subunits modified glutenin aggregation, but glutenin properties were much more affected by expression of the 1Dx5 transgene. This resulted in increased cross-linking of glutenin polymers. In dynamic assay, the storage and loss moduli of hydrated glutens containing 1Dx5 transgene subunits were considerably enhanced, whereas expression of the 1Ax1 transgene had a limited effect. The very high strength of 1Dx5 transformed glutens resulted in abnormal mixing properties of dough. These results are discussed with regard to glutenin subunit and glutenin polymer structures.     

Rheological Properties of Full-Formula Doughs Derived from Near-Isogenic 1BL/1RS Translocation Lines

Four pairs of near-isogenic wheat lines, with and without the 1BL/1RS translocation, and differing at the Glu-1 loci (coding for high molecular weight [HMW] glutenin subunits) were evaluated for their dough mixing properties, dough stickiness, and baking performance. In all 1BL/1RS translocation lines, weakening of the dough consistency occurred within 2 min past peak time. The full-formula dough from every 1BL/1RS translocation line exhibited poor dough mixing characteristics and increased stickiness compared to the corresponding wheat control. The HMW glutenin subunits coded by the Glu-A1 locus had no apparent effect on mixing properties, but did have a slight effect on the dough stickiness at two of the four stages of dough mixing. Glu-B1 and Glu-D1 loci encoded glutenin subunits produced significant changes in dough mixing properties and dough stickiness, respectively. With respect to baking performance, there was no significant difference between loaf volumes of 1BL/1RS versus control wheats for three of four near-isogenic pairs. Within the 1RS-group, the translocation lines containing HMW glutenin subunits 5+10 produced bread with greater loaf volumes than the pairs containing its allelic counterpart 2+12. Loaf volume was not influenced by the subunits associated with the Glu-B1 loci. In general, the breads baked from 1BL/1RS translocation lines had a relatively poor crumb and crust quality and contained larger gas cells than the wheat controls. In comparing isogenic pairs, the magnitude of the difference in loaf volume between the control wheat and the corresponding 1BL/1RS translocation line was greater in the pair unique for HMW subunits 5+10; the difference was primarily due to the stronger mixing properties of the wheat control.     

Heat-Shock Protein 70 and Dough-Quality Changes Resulting from Heat Stress During Grain Filling in Wheat

In an attempt to further elucidate the molecular mechanisms that determine the loss of dough strength associated with heat stress of growing wheat, the roles of heat-shock proteins (HSP) and heat-shock elements upstream of glutenin genes were investigated. A range of genotypes differed in the extent of synthesis of high molecular weight glutenin subunits (HMW-GS) and HSP during heat stress. The concentration of HSP 70 remaining in mature grain increased as a result of a few days' heat stress of wheat plants. The amount of HSP 70 in mature grain samples from heat-stressed plants of 45 genotypes was not strongly correlated with loss of dough strength. There was much less evidence for this mechanism than for other molecular hypotheses from the literature, particularly, changes in glutenin-to-gliadin ratio, size distribution of the glutenin polymer, and the involvement of HSP and chaperones during grain-protein synthesis. HSP 70 was purified from heat-stressed grain, and was added to (or incorporated into) dough in the direct-drive mixograph. The HSP behaved similarly to several other hydrophilic proteins when added at a level of 2 mg/2 g of flour. It showed no dramatic effects on dough properties that could constitute a major explanation for the dough-weakening effects of heat stress, even though the level of addition was well above the maximum levels that might be encountered in field-grown, mature grain. Furthermore, sequencing of the genes (upstream of the coding region) for HMW-GS failed to show the presence of heat-shock promoters, even for genotypes that differed considerably in their reactions to heat stress. The findings simplify the range of possibilities that cause heat-related loss of dough strength, focusing attention on the degree of polymerization of the glutenin chains, and on the roles of HSP and chaperones in the developing grain.